Process for treating the surface of aluminium or aluminium alloy with an organohydrogenpolysiloxane



United States Patent 3,274,078 PROCESS FOR TREATING THE SURFACE OF ALU-MINIUM 0R ALUMHNIUM ALLOY WITH AN OR- GANOHYDROGENPOLYSILOXANE YujiTsuji, Shinagawa-kn, Tokyo-to, Japan, assignor to Tokyo Shibaura DenkiKabushiki Kaisha, Kawasakishi, Japan, a joint-stock company No Drawing.Filed Sept. 11, 1962, Ser. No. 222,963 Claims priority, applicationJapan, Oct. 6, 1961, 36/ 35,865 3 Claims. (Cl. 204-35) This inventionrelates to a process for treating the surface of a metal consistingessentially of aluminum, and more particularly to a process for treatingthe surface of the metal to reduce the tendency of ice to adherethereto.

It is well known that it is desirable for ice trays for use inrefrigerators to be made of electrolytically anodized aluminum. However,owing to the strong tendency of ice to adhere to the surface of anodizedaluminum, it is necessary to coat such a surface with a durable film forminimizing adhesion of ice thereto. For example, a process for treatingthe surface of aluminium has been proposed, wherein an o'rganosiliconecompound containing a silicon bonded hydroxy radical is applied to thesurface of anodized aluminium and then an over coating comprising apolyorganohalogenopolysiloxane is applied to the treated surface. Whilethis process of surface treatment substantially reduces the tendency ofice to adhere to the surface of aluminum it is complicated and costly,as it requires two separate steps, viz., the step of applying a basecoating and the step of overcoating.

Accordingly, an object of this invention is to provide a simple processfor treating the surface of a metal consisting essentially of aluminiumwhich can not only improve anti-corrosion and anti-wearing properties ofthe surface but also permanently minimize the tendency of ice to adhereto it.

A more specific object of this invention is to provide a novel processfor treating the surface of a metal consisting essentially of aluminiumto minimize the tendency of ice to adhere thereto without requiring thestep of providing a base coating. The novel process comprises forming ananodic film on the surface of the metal by electolytically anodizing themetal in an organic or inorganic acid such as oxalic acid or sulfuricacid and applying to the anodized surface a film of a particularorganopolysiloxane having the property of resisting the adherencethereto of ice.

This invention is based on the discovery that the substantial number ofOH groups remaining in anodic film just after it has been formed effectsa dehydrogenation reaction with an organohydrogenpolysiloxane which isapplied thereon by painting or by impregnation immediately after saidanodizing process, thus firmly anchoring said organohydrogenpolysiloxaneto the anodic film through chemical bonding.

Thus, this invention relates to a process for treating the surface of ametal consisting essentially of aluminum characterized byelectrolytically anodizing said surface to form an anodic film thereon,applying an organohydrogenpolysiloxane on the anodized surfaceimmediately subsequent to the formation thereof, and then heating.

The following are several examples of this invention, but it is to beunderstood that this invention is not to be limited thereto but can becarried out in various other ways without departing from the true spiritas defined in the appended claims.

Example 1 An ice tray of aluminium, 2S Alco grade for use in householdrefrigerators was electrolytically anodized in "ice a bath of sulphuricacid in a manner well known in the art to form an anodic film of 15microns thickness on the surface of the ice tray. Immediately after theanodizing step, the ice tray was washed with water, and water wasremoved from the surface of the ice tray by wiping. Then the ice traywas immersed in 25 perecnt benzene solution ofmethylhydrogenpolysiloxane for about one minute. After removal from saidsolution, the ice tray was air dried to evaporate olf benzene, and wastreated with steam at a pressure of at about four atmospheres for about20 minutes to form a smooth transparent film on the surface of the icetray. Ice cubes made in this ice tray mounted on an evaporatormaintained at --6 C. were easily removed with relatively small force,and even after repeated removal of 100 times or more, it was found thatthe ice cubes were released as easily as the first time with equallysmall force. Anti-wearing and anti-corrosion tests made on the above icetray in accordance with the 118 Japanese Industrial Standard H 8601testing method showed that these properties were over 350 seconds andseconds, respectively, which are to be compared with 230 seconds and 50seconds, respectively, of a prior ice tray having anodic film only.

Example 2 An ice tray of a machined die cast aluminium, 13 Alcoa gradewas electrolytically anodized to form an anodic film of 20 micronsthickness and washed with water, and the water remaining on the surfaceof the ice tray was wiped off. Immediately thereafter, a 12.5 perecntxylene solution of a methylhydrogenpolysiloxane was applied to thesurface of the ice tray and dried. Then the ice tray was heat treated inboiling water at C. for about 40 minutes to obtain a smooth transparentfilm. Ice cubes made in this ice tray at 5 C. were removed withrelatively small force, and it was found that the ice releasing propertyremained substantially unchanged after repeated removal of over 200times. Antiwear property and anticorrosion property were again improvedas in Example 1.

Example 3 An evaporator made of aluminium blank, 38 Alcoa grade commonlyutilized in household refrigerators was electrolytically anodized in asuitable manner to form an anodic film of 25 microns thickness.Immediately following the anodizing step, the evaporator was washed withwater, and, after removal of water by using absorbent cotton impregnatedwith a 12.5 percent toluene solution of methylhydrogenpolysiloxane, washeat treated in an air drying furnace maintained at 120 C. for about 15minutes to obtain a smooth transparent film. An ice block made on thisevaporator at -7 C. was easily removed with relatively small force, andit was found that the ice releasing property remained substantiallyunchanged after repeated removal of over 300 times. Again, wearresistive and corrosion resistive properties were improved as in theforegoing examples.

Example 4 The same ice tray as in Example 1 was anodized in a bath ofsulphuric acid to form an anodic film of 15 microns thickness, washed inwater, and water was removed from the tray. Immediately thereafter theice tray was dipped in a 9.5 percent benzene-butanol solution ofethylhydrogenpolysiloxane. After removal from the solution, the ice traywas subjected to a heat treatment similar to that of Example 1. This icetray was mounted on an evaporator maintained at 7 C., and test of icecube removal was repeated 100 times. Even at the end of the test, icecubes were released as easily as at the first time with substantiallythe same small force. In this case, too, anti-wearing property andanti-corrosion property were improved as in the foregoing examples.

Example 5 An ice tray of die cast aluminium similar to that of Example 2was similarly electrolytically anodized to form an andoic film of 20microns thickness and washed with water. After drying, a 9.5 percentbenzene solution of phenylhydrogenpolysiloxane was applied to thesurface of the tray and dried. Then the tray was dipped in boiling waterat 100 C. for about 40 minutes. The finished ice tray was mounted on anevaporator maintained at -7 C. to freeze water contained therein, andtest of ice cube removal was repeated 100 times. It was found thatreleasability of ice cubes was substantially the same throughout thetest and that the anti-wear and the anti-corrosion properties were alsoimproved as in the foregoing examples.

On the other hand, ice trays made of aluminium or its alloy which wereelectrolytically anodized in usual manner to form an anodic film andtreated by steam to seal interstices in the anodic film and thereafterprovided with a film of methyl-, ethylor phenylhydrogen-polysiloxane, asin the proceeding examples, showed marked decrease in the ice cubereleasability after repeated removal of only 20 times.

While this invention has been described in connection with preferredexamples thereof, it will be understood that this invention can bemodified in various ways without departing from the true spirit andscope of the invention as defined in the appended claim. For example,edges of airplane wings, components, of ship parts, and the like, mayalso be treated with the process of this invention.

What is claimed is:

1. Process for treating the surface of a metal consisting essentially ofcomprising the steps of forming a porous film of aluminum oxide byelectrolytically anodizing said metal, applying anorganohydrogenpolysiloxane onto said porous film of aluminum oxideimmediately after said anodizing step and then heating said thus-treatedmetal surface.

2. A process for treating the surface of a metal consisting essentiallyof aluminum, which comprises the steps of forming an anodic film byelectrolytically anodizing said metal, applying a solution of anorganohydrogenpolysiloxane selected from the group consisting ofmethylhydrogenpolysiloxane, ethylhydrogenpolysiloxane, andphenylhydrogenpolysiloxane onto said anodic film immediately after saidanodizing step and then heating said surface, thus-coated, in order tochemically bond organopolysiloxane to said metal surface.

3. A process for treating the surface of a metal consisting esesntiallyof aluminum which comprises the steps of forming an anodic film on thesurface of said metal by electrolytically anodizing said metal, washingwith water and drying the thus-treated metal surface, applying anorganohydrogenpolysiloxane selected from the group which consists ofmethylhydrogenpolysiloxane, ethylhydrogenpolysiloxane, andphenylhydrogenpolysiloxane to said thus-treated metal surface andheating the organohydrogenpolysiloxane coated metal surface in order tochemically bond said metal surface with said organohydrogenpolysiloxane.

References Cited by the Examiner UNITED STATES PATENTS 2,537,433 1/1951Waring 126---19 2,575,141 11/1951 Smith-Johannsen 62357 2,683,113 7/1954France et al. 204--38 2,961,110 11/1960 Cooke et .al. 117-135.12,978,098 4/1961 Post 117135.1

OTHER REFERENCES Wernick: Finishing of Aluminium, pages 354-363 JOHN H.MACK, Primary Examiner.

MURRAY TILLMAN, Examiner.

L. G. WISE, W. VAN SISE, Assistant Examiners.

1. PROCESS FOR TREATING THE SURFACE OF A METAL CONSISTING ESSENTIALLY OFCOMPRISING THE STEPS OF FORMING A POROUS FILM OF ALUMINUM OXIDE BYELECTROLYTICALLY ANODIZING SAID METAL, APPLYING ANORGANOHYDROGENPOLYSILOXANE ONTO SAID POROUS FILM OF ALUMINUM OXIDEIMMEDIATELY AFTER SAID ANODIZING STEP AND THEN HEATING SAID THUS-TREATEDMETAL SURFACE.